Dynamic attributes (getters/setters) in Swift on data models - swift

Question

I'm trying to use Swift (which I'm very new at) to create a clean interface for my data models. These models are backed by Firebase (though this is ultimately irrelevant to the actual question). What I want to avoid is writing tons of setter/accessor boiler plate code over and over.
For example:
class MyData {
let connection: Firebase!
private var _name: String? // internal storage, like an iVar in ObjC
init(connection: Firebase!) {
self.connection = connection
self.connection.observeEventType(.Value, withBlock: { snapshot in
_name = snapshot["name"]
}
}
var name: {
get {
return _name
}
set(name) {
// When the client sets the name, write it to Firebase
_name = name
self.connection.childByAppendingPath("name").setValue(name)
}
}
}
I'm sure I'm making a lot of mistakes in there. The idea is that the data is first loaded from the server when the instance is instantiated. Subsequently, we could call my_data_instance.name to get that name, or my_data_instance.name = "foo" and the name would be automatically written to the server.
This requires ~10 lines of code for a single attribute (of which there will be many). Nuts! There must be a better way!
EDIT: to be clear, I want to obviate the need to write as MUCH boiler plate code as possible. Consider a library like Mantle, where merely defining a #property is sufficient to do everything you want. In my opinion, anything more than one single line of code to say I have an attribute called "name", handle it via Firebase is overly verbose.

Answer 1

You can use Key-Value Observing to monitor changes in your properties. More info in Adopting Cocoa Design Patterns in Swift.
import Foundation
private var KVOContext = 0
// Your class must inherit from NSObject
class MyData : NSObject {
private let propertiesToObserve = ["name", "location"]
dynamic var name: String
dynamic var location: String
init(name: String, location: String) {
self.name = name
self.location = location
super.init()
// Add the properties that you want to observe
for property in self.propertiesToObserve {
self.addObserver(self, forKeyPath: property, options: [.New, .Old], context: &KVOContext)
}
}
// This method is called whenever an observed property is changed
override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
if let property = keyPath,
newValue = change![NSKeyValueChangeNewKey],
oldValue = change![NSKeyValueChangeOldKey] {
print("\(property) changed from \(oldValue) to \(newValue)")
// If oldValue != newValue, write back to Firebase
}
}
// Remove self as observer of self
deinit {
for property in self.propertiesToObserve {
self.removeObserver(self, forKeyPath: property)
}
}
}
let data = MyData(name: "John", location: "Chicago")
data.name = "David" // print: name changed from John to David
data.location = "New York" // print: location changed from Chicago to New York

Answer 2

Swift provides that functionality called property observer
var name: String {
didSet {
self.connection.childByAppendingPath("name").setValue(name)
}
}
There is a second observer willSet which is called before the value is changed.
Note (from the documentation):
When you assign a default value to a stored property, or set its
initial value within an initializer, the value of that property is set
directly, without calling any property observers.